Along with the development of modern data communications, demands for broadband service transmission are presented to network operators as well as challenges. Existing Synchronous Digital Hierarchy (SDH)/Synchronous Optical Networking (SONET) transmission networks have insufficient resources to transmit huge data flows generated by Internet Protocol (IP) core routers and Asynchronous Transfer Mode (ATM) exchanges. To satisfy the demands of broadband service transmission, a method in which existing devices will not be replaced is needed.
The largest Virtual Container (VC) in the existing transport network is VC-4. Although VC-4 belongs to a higher order VC, the only available transmission service bandwidth is 140 Mbps. With the development of ATM and IP networks, demands for bandwidth have already exceeded the capacity provided by one VC-4. According to several techniques developed so far, the bandwidths of multiple VC-4s can be combined to provide an interface with a high bandwidth to transmit broadband services.
A Contiguous Concatenation means that contiguous Container-n (C-n) (five standard containers are defined by G.709, which are C-11, C-12, C-2, C-3 and C-4) in one Synchronous Transmission Module level n (STM-N) are concatenated as a C-n-XC to form a whole structure to perform the transmission. The STM-N is a frame structure of an Synchronous Digital Hierarchy (SDH) signal, which is a block frame structure of 9 rows*270*N columns, and Telecommunication Standardization Sector of International Telecommunication Union (ITU-T) defines that the frame of STM-N is in a rectangle and block structure adopting a byte as a unit. It can be seen that the contiguous concatenated C-4-XC has only one column of Path Overhead (POH) indication, therefore a continuous bandwidth thereof must be maintained in the entire transmission process. The above technology needs support of all the devices by which the transmission passes in the network, whereas the majority of existing devices do not possess the capability.
A virtual concatenation means that VC-ns distributed in different STM-Ns are concatenated to form a VC-n-Xv, i.e., to form a VCG to perform the transmission. The VC-ns may be in the same route or in different routes. Each C-n in the VCG has an independent structure, i.e., has its own POH as well as an entire structure of VC-n. The virtual concatenation of several C-ns is equal to several interleaved VC-ns. It is only needed to provide special hardware support at the two ends of the concatenation in terms of the device.
The Link Capacity Adjustment Scheme (LCAS) is one of the technologies employed in virtual concatenation and capable of improving the performance of virtual concatenation, of which the basic principle is to utilize a reservation overhead byte of the SDH (the H4 bytes are utilized in the case of the higher order virtual concatenation, while the K4 bytes are utilized in the case of the lower order virtual concatenation) to transfer control information, so as to dynamically adjust the amount of VCs used for mapping the needed service to adapt to different demands for service bandwidth and increase bandwidth utilization. The LCAS protocol brings the following advantages: the network is more robust, the service may not be affected when the capacity of the VCG is adjusted, damaged link, i.e., the link where there is a failure, can be shielded initiatively so as to guarantee the service transmission, and when the damaged link recovers to a normal state, it can be utilized again to resume the bandwidth.
For better understanding, meanings of specific terms are defined as follows:
Link: a connection from one end to the other end in the network, corresponding to a group of members in the VCG, i.e., corresponding to the VCG itself An entire link includes an uplink and a downlink according to the transmission direction of data, and the data are transmitted from the uplink to the downlink.
Member: an individual container that belongs to a VCG.
VCG: a combination of a group of members related with each other, which is a logic link group with a higher capacity.
Source (So): a device end to transmit the data, i.e., an originating device end where the uplink is located.
Sink (Sk): a device end to receive the data, i.e., the device end where the downlink is terminated.
Both the So and the Sk possess the LCAS capability, i.e., each of them possesses a Link Capacity Adjustment Scheme Controller (LCASC). An uplink member hereinafter refers to a member of the VCG in the So LCAS device, and correspondingly, a downlink member refers to a member of the VCG in the Sk LCAS device.
The technical solution in the prior art supports the reduction of the capacity of a VCG in the manner of command, the command supported include: a command to reduce the capacity (to remove the members), including an uplink-member removing command and a downlink-member removing command.
As the existing solution defines only a method to reduce the capacity, i.e., to remove the members, in which the uplink member should be removed before the downlink member is removed, while no method in which the downlink member is removed before the uplink member is removed has been defined, there is a sequence requirement for supporting the two commands mentioned above to reduce the capacity (the uplink-member removing command and the downlink-member removing command). When a member is about to be removed, the uplink-member removing command must be used before the downlink-member removing command is used. An implementation method in the prior art to reduce the capacity of the VCG, i.e., to remove members in the VCG, is described in detail hereinafter.
FIG. 1 is a sequence chart illustrating the process to remove a member which is not the last one in a VCG in accordance with the related art. Member 4 (Mem 4) and Mem 5 will be removed from a VCG including 6 members, i.e., the multiple members to be removed do not include the last one in number in the VCG. The LCAS in the sequence chart is an So LCASC, which is the So of Mem 4, Mem 5 and Mem 6 at the same time, whereas the Sks of the three members are different devices.
Referring to FIG. 1, a Network Management System (NMS) sends an uplink-member removing command to the So LCASC, instructing it to remove the uplink members corresponding to Mem 4 and Mem 5 in the sequence chart, i.e., to remove the uplink members of the So, Mem 4 and Mem 5. The So sends CTRL=IDLE and Sequence Indicator (SQ)=4 to Mem 4 of the Sk, sends CTRL=IDLE and SQ=5 to Mem 5 of the Sk, and sends CTRL=End of Sequence (EOS) and SQ=3 to Mem 6 of the Sk. Upon receiving CTRL=IDLE, Mem 4 and Mem 5 of the Sk reorganize the service, and the removed members will not be used any longer. Then the Sk returns state information indicating the member state as failure and information indicating the changed member sequence to the So, i.e., return Member State (MST)=FAIL and Re-Sequence Acknowledge (RS-Ack) inverted information to the So. After that, Mem 4 and Mem 5 of the So are removed from the VCG, i.e., the capacity of the VCG is reduced, and Mem 6 becomes the last available member in the VCG, correspondingly, the SQs of previous Mem 4, Mem 5 and Mem 6 have changed.
Thus, the members of the So have been removed, i.e., the uplink members Mem 4 and Mem 5 have been removed.
Since the corresponding members of the Sk, i.e., downlink members Mem 4 and Mem 5, have already been in the failure state and will no longer be a service bearer, Mem 4 and Mem 5 of the Sk can be removed at this point. The specific process is that the NMS sends a downlink-member removing command to the Sk directly, and the Sk removes Mem 4 and Mem 5 directly. Certainly, Mem 4 and Mem 5 of the Sk may not be removed because they are already in the failure state and will not be used any longer.
Certainly, a response from the Sk to the So only aims to confirm that the member will not be used as an Sk any longer, if necessary, the NMS can perform a de-provisioning operation for the member. No de-provisioning operation is described in the sequence chart above.
A general principle to adjust the SQs in a REMOVE (REM) function includes: all the unnecessary members are re-assigned with an SQ higher than that of the member to which CRTL=EOS is sent; and
all the members necessary to be reserved are re-assigned with multiple continuous SQs which are lower than that of the unnecessary members.
For example, suppose that a certain VCG includes seven members from A˜G, the SQs thereof are from 0˜6 respectively. When members C, D and G are removed, the SQ of each member in the VCG before and after the removing is shown in Table 1.
TABLE 1VCABCDEFGBefore adjustmentSQ0123456UUUAfter adjustmentSQ0145236
FIG. 2 is a sequence chart illustrating the process to remove the last member in a VCG in accordance with the related art. The specific operation is nearly the same as that shown in FIG. 1, thus no detailed descriptions will be given. Compared with the operation illustrated in FIG. 1, the difference is that the So sends sequence terminal configuration information to the last member but one in number in the VCG after the removing operation is finished.
It can be seen that, in the existing process to remove the members, since only the method in which the uplink members are removed first is defined, when the capacity of the VCG is changed, particularly when the operation to reduce the capacity of the VCG is performed, the uplink members must be removed before the downlink members are removed. That is to say, the NMS may send the removing command to the So first instead of sending the removing command to the Sk first. As a result, a strict restriction is brought to an operation mode of the operator, i.e., the uplink-member removing command must be issued before the downlink-member removing command is issued.
In case of mis-operation of the operator, which makes the NMS issue a downlink-member removing command first, i.e., the removing command is sent to the Sk first, then the LCAS negotiation mechanism will be damaged, making the downlink members removed directly while the corresponding uplink members are not informed, which will lead to a link failure, e.g., a failure in service de-encapsulation and the like. As a result, the corresponding uplink members are unable to perform the negotiation with the downlink members such that the uplink members could not be removed. That is to say, if the operator works by mistake, i.e., issues a downlink-member removing command first, there will be a negative impact on the entire virtual concatenation service, leading to, e.g., an interrupted service that makes the LCAS lose the protection function.